All nuclear power plants have some form of emergency core cooling system (ECCS). In the event that normal operation is lost, a major break can occur in the reactor coolant system. This is generally referred to as a loss of coolant accident (LOCA). There are two phases to most ECCS—the injection phase when the pumps suction water from a large tank and pump that water to spray the general primary containment area, or directly into the reactor coolant system or reactor, and the recirculation phase when the pumps take water from the containment sump after all of the available water inventory in the storage tanks has been pumped into the containment.
An ECCS has one major function and that is to provide makeup water to cool the reactor in the event of a LOCA from the reactor coolant system. This cooling is needed to remove the heat in the reactor's core, allowing to reactor to achieve a state of safe cold shutdown.
The major components of an ECCS are pumps, interconnecting piping, high pressure pumps, low pressure pumps, water storage tanks, accumulators, and a containment sump used to circulate the water through the reactor once the storage tanks are empty.
In a nuclear power plant, a suction strainer is located in the containment area, and its purpose is to keep loose materials and debris, such as insulation, from getting to the suction of the ECCS pumps during the recirculation phase. The pumps perform an important and vital function at nuclear power plants. Again, a purpose of the strainers is to protect the downstream components, such as pumps and nuclear fuel assemblies, from being adversely affected by such debris. Suction strainers, by their nature, have a tendency to build up debris layers. In use, as water is circulated through the strainer, solid debris builds on the outer surfaces of the strainer. The recirculation generally continues until the ECCS is no longer needed in cold shutdown.
Since the ECCS system may need to function for many hours, days and even weeks, it is important to ensure that the suction strainers continue to allow flow through the ECCS system; therefore, it is equally important that the amount of debris reaching those suction strainers is minimized to ensure continued operability.
Fibrous, block and blanket-type insulations are frequently used in power plants to conserve thermal energy within the insulated piping or equipment during normal operation. In many situations, the insulation is covered by removable/reusable stainless steel jacketing that uses latches for attachment.
These insulation systems are not immune from damage and can disintegrate under impact from a LOCA. This could cause undesirable release of insulation debris which could adversely affect the performance of the ECCS. Destruction of thermal insulation can be considerably reduced when it is encapsulated by stainless steel jackets, and when that stainless steel jacketing itself is not dislodged. It is, therefore, important to maintain the stainless steel jacketing around the insulation when a LOCA occurs to reduce the generation of debris and limit the transportation of this same debris to the suction strainer.
Jacketing is typically installed with attachment hardware such as screws or blind rivets. Jacketing may also be secured by banding with latches or other retaining methods. However, banding is typically installed as a component that is separate and distinct from the jacketing system. During a severe accident in a nuclear power plant, such as a LOCA, the destructive forces from escaping saturated steam and water can cause the jacketing to deform underneath the banding. With no fixing arrangement between the jacketing and the banding, the jacketing, and subsequently the underlying insulation, can be destroyed. Banding can be attached to the jacketing by screws or blind rivets, but these negate the removability feature of the jacket needed for plant personnel to remove and replace insulation for inspections and maintenance on a regular basis.
The present invention is provided to solve the problems discussed above. A full discussion of the features and advantages of the present invention is deferred to the following detailed description, which proceeds with reference to the accompanying drawings.